A Study of Diarrhea and Intestinal Flora Changes Caused by Pyrotinib in Breast Cancer

Inclusion Criteria: 1. Female breast cancer patients aged 18-75 years. 2. ECOG performance status of 0 to 1; 3. Known hormone receptor status; 4. HER2 positive breast cancer and previously reveived ≤2 anti-HER2 therapy; 5. Breast cancer patients are about to receive pyrotinib monotherapy or combined with Trastuzumab/Inetetamab and chemotherapy； 6. Patients with adequate organ function before enrollment (no blood transfusion, no white blood cell or platelet-elevating drugs used within 2 weeks before screening): 1) Blood routine:ANC≥1.5×10\^9/L; PLT≥90×10\^9/L; Hb≥90 g/L；2)Blood biochemistry: TBIL≤1.5×ULN;ALT and AST ≤1.5×ULN; alkaline phosphatase ≤ 2.5×ULN; BUN and Cr≤1.5×ULN；3) Cardiac color Doppler ultrasound:LVEF≥55%；4) 12-lead ECG: QTcF \< 470 msec; 7. Signed the informed consent form prior to patient entry, and have good compliance and are willing to cooperate with follow-up. Exclusion Criteria: 1. patients with Severe heart disease or discomfor; 2. Previous or ongoing use of HER2-targeted tyrosine kinase inhibitors ; 3. Inability to swallow, intestinal obstruction, or other factors that affect the taking and absorption of the drug; 4. Allergy to pyrotinib; history of immunodeficiency, including HIV positive, active HBV/HCV, other acquired or congenital immunodeficiency disease and organ transplantation history; 5. Patients during pregnancy or lactation, patients with childbearing potential tested positive in baseline pregnancy test, or patients unwilling to take effective contraceptive measures throughout the trial and 7 months after the last study medication; 6. patients with intestinal disease, serious concomitant diseases, or other comorbid diseases that will interfere with the planned treatment, or patients not eligible for this study judged by the investigator.